X-ray Absorption Spectroscopy Investigations of Copper(II) Coordination in the Human Amyloid β Peptide

Abstract

Alzheimer’s disease (AD) is the main cause of age-related dementia and currently affects approximately 5.7 million Americans. Major brain changes associated with AD pathology include accumulation of amyloid beta (Aβ) protein fragments and formation of extracellular amyloid plaques. Redox-active metals mediate oligomerization of Aβ, and the resultant metal-bound oligomers have been implicated in the putative formation of harmful, reactive species that could contribute to observed oxidative damage. In isolated plaque cores, Cu­(II) is bound to Aβ via histidine residues. Despite numerous structural studies of Cu­(II) binding to synthetic Aβ in vitro, there is still uncertainty surrounding Cu­(II) coordination in Aβ. In this study, we used X-ray absorption spectroscopy (XAS) and high energy resolution fluorescence detected (HERFD) XAS to investigate Cu­(II) coordination in Aβ(1–42) under various solution conditions. We found that the average coordination environment in Cu­(II)­Aβ(1–42) is sensitive to X-ray photoreduction, changes in buffer composition, peptide concentration, and solution pH. Fitting of the extended X-ray absorption fine structure (EXAFS) suggests Cu­(II) is bound in a mixture of coordination environments in monomeric Aβ(1–42) under all conditions studied. However, it was evident that on average only a single histidine residue coordinates Cu­(II) in monomeric Aβ(1–42) at pH 6.1, in addition to 3 other oxygen or nitrogen ligands. Cu­(II) coordination in Aβ(1–42) at pH 7.4 is similarly 4-coordinate with oxygen and nitrogen ligands, although an average of 2 histidine residues appear to coordinate at this pH. At pH 9.0, the average Cu­(II) coordination environment in Aβ(1–42) appears to be 5-coordinate with oxygen and nitrogen ligands, including two histidine residues.

Redox state and photoreduction control using X-ray spectroelectrochemical techniques – advances in design and fabrication through additive engineering

“…The OCP value depends on the standing concentration and chemical activity of the oxidised and reduced products and together with the conditioning of the electrode, this depends on the beam intensity and the flow properties of the solution. The negative shift of the OCP indicates more reducing conditions and is consistent with the reported proclivity of copper(II) complexes to photoreduction (Summers et al, 2019, Stellato et al, 2019. The response of the OCP to a change in beam intensity is reflected by the highly reproducible signature associated with the start of each scan.…”

“…Rapid freezing of the solution, after addition of cryoprotectants designed to reduce crystallisation, reduces significantly the sample volume requirements and can produce a sample which is more robust in terms of photoreduction, although problems commonly persist for absorbers such as Cu, As and Se (George et al, 2012). This is well illustrated by recent studies into the impact of photoreduction of Cu-bound amyloid  peptide (CuAß) samples have examined both the time/flux dependence of sample degradation and the impact of cryoprotectants (Summers et al, 2019, Stellato et al, 2019, Streltsov et al, 2008.…”

Modelling the efficacy of Neprilysin from various species in degrading different Amyloid-β peptides: Potential application in therapeutics of Alzheimer’s disease

“…14–17 Depending on the variation in the site of cleavage in the amyloid precursor protein a variety of Aβ peptides can be generated, which may impact the pathophysiology of AD differently. 17–19 The variable nature of Aβ peptides will influence the extent to which they are further enzymatically degraded by neprilysin. As shown in this study considerable variation in the affinity and efficacy of different recombinant human neprilysin against Aβ peptides was observed.…”

Copper Toxicity Links to Pathogenesis of Alzheimer’s Disease and Therapeutics Approaches

“…Multivalent metal ions such as copper (Cu) [ 64 , 65 , 66 ], zinc (Zn) [ 67 , 68 ], and iron (Fe) [ 69 , 70 ] are reported to be at higher levels in Alzheimer’s senile plaques [ 71 , 72 ]; while the connection of these metal ions with Aβ aggregation is still not well known. Indeed, some evidence from transgenic animal studies shows that Cu accumulates in senile plaques in the brains of 5 × FAD and Tg-SwDI/NOS2−/− mice models with neurodegeneration, as compared to PSAPP, where no Cu deposition has been seen among the mice with less neurodegeneration [ 73 ].…”